The instances of single vehicle roadway crashes comprise approximately 20 percent of all light vehicle crashes annually in the United States. Within the single vehicle roadway departure crash category, crashes result from four basic categories: lane drifting, control loss, evasive maneuvers, and driver incapacitation. Countermeasures that can attempt to address these crash categories are derived from a variety of sensor systems. Lane drift warning is, in certain circumstances, conventionally addressed by computer vision lane trackers that perform best when the vehicle is slowly drifting toward or across the road edge.
There may be two issues associated with the potential effectiveness of lane tracker based drift warning. The first is due to not always being able to visually track the lane markers. The other is the situation where the vehicle crosses the road edge with high lateral speed such that a warning is of little use to the driver. The high relative lateral speed is usually the result of vehicle control loss or driver evasive maneuvers. Evasive maneuvers, like driver incapacitation, are difficult to address with countermeasures since the driver is occupied or otherwise distracted.
Control loss, on the other hand, may result from excessive speed for the road or road conditions. Control loss in curved road sections may be mitigated by a system that aids the driver in entering a curve at a passable speed. The required forward sight distance, however, may be prohibitive for reliable computer vision based detection of upcoming curves.